Means for translating magnetic variations into electric variations



July 11, 1939. A. M. SKELLETT MEANS FOR TRANSLATING MAGNETIC VARIATIONSINTO ELECTRIC VARIATIONS Filed March 31, 1957 IN I/E N TOR AM SKELLETTBr ATT RNE'V UNITED STATES PATENT err-ice 2,165,307 MEANS FOR.TRANSLATING MAGNETIC VA- RIATIONS IN TO ELECTRIC VARIATIONS Albert M.Skellett, Madison,

N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York,N. Y., 'a corporation of New York Application March 31, 1937, Serial No.134,067

22 Claims.

This invention relates to means for transforming magnetic variationsinto electric variations and more specifically to means for reading amagnetic record upon which signals representative of the light-tonevalues of a picture or view are recorded.

When an ordinary magnetic pick-up device is used for reading a magneticrecord, the currents delivered by the pick-up coil have all been shiftedin phase by degrees from that of the original current. This is caused bythe fact that in the magnetic pick-up the output current is proportionalto the rate of change of flux rather than to the flux itself. This shiftin phase of 90 degrees is not important in the case of sound recordingas the human ear is insensitive to this shift. In the case of televisionimage currents, however, the shift is enough to make the imageunrecognizable because a shift of 90 degrees is a variable shift withrespect to time even though it is a constant angular shift. For example,a shift of 90 degrees for a 30-cycle signal is a displacement in time of1/ of a second, while a shift of the same phase angle for a 5000-cyelesignal is a time displacement of only 1/20,000 of a second. i

It is an object of this invention to provide a reading or translatingdevice for a magnetic record which does not produce the above mentionedphase shifts and which is suitable for use with records of signalsrepresentative of a picture or view which is to be reproduced in theform of a facsimile or image by television methods.

It is a further object of the invention to provide inductionless meansfor translating magnetic variations into variations of an electronicbeam. v

Another object is to provide means for translating magnetic variationsinto electric current variations the amplitudes of which areproportional to those of the magnetic variations and not dependent uponthe frequency of the latter. In the ordinary magnetic pick-up deviceused to translate a magnetic record and similar devices used. elsewherefor translating magnetic variations into electric variations, theamplitudes of the electric var ations are in part dependent upon thefrequency of the variations, thus producing distortion of the currentvariations.

In an embodiment of the invention which is given by way of example toillustrate the invention, a yoke of soft iron is set up around a cathoderay tube adjacent some pole-pieces of similar material therein in such amanner that there are two gaps in the magnetic circuit (in addition tothe gaps filled by the walls of the tube), one just large enough for themagnetic tape or other movable means carrying magnetic variations topass therethrough and the other through which the electron beam passes.No magnetic coils are used on this yoke which serves to guide themagnetic flux from the tape directly to and into the cathode ray tube soas to deflect the cathode ray beam in such a manner that it divides itsenergy between a pair of anode plates connected in pushpull manner. Arelatively small accelerating voltage, that is, of the order of hundredsof volts or less, is preferably used for accelerating the beam generatedin the cathode ray device so that the beam is appreciably bent for thesmall fluxes available. The two anode plates are preferably connected,in opposition, to the primary winding of a transformer, the mid-point ofwhich is connected through a battery to the accelerating anode of thecathode ray tube. The output current in the secondary winding of thetransformer is thus always substantially in phase with the flux in themagnetic tape and the amplitude is independent of the frequency of thesignal. Another advantage of this arrangement is the high output due tothe amplification of the original energy because the entire energy ofthe electron beam is controlled by the small fiux in the tape.

It is found that this device operates satisfactorily when the yoke is ofsoft iron but a preferred material is permalloy or other similarmaterial having high permeability at low magnetizing forces.

The invention will be more readily understood from the followingdescription taken in connection with the accompanying drawing forming apart thereof, in which:

Fig. 1 is a perspective view of an electronic pick-up device formagnetic recording;

Fig. 2 is a transverse cross-sectional view of the device shown in Fig.1; and

Fig. 3 is a longitudinal cross-sectional view of the device shown inFig. 1 taken from the top.

Referring more particularly to the drawing, Fig. 1 shows in perspectivean electronic pick-up device for reproducing signals previously recordedon a magnetic tape. The electronic pick-up arrangement comprises a tapel0 adapted to be passed through a narrow gap I I in a magnetic circuitl2 through a second gap 53 of which the beam generated in a cathode raydevice I3 is adapted to pass, the deflection of the beam beingcontrolled by the signals on the magnetic tape. The record member I0 ispreferably a tape or any suitable magnetic material about .001 inchthick and .125 inch wide, the ends of which are secured to and wound onreels l4 and I5, respectively. The tape has been previously magnetizedwith signal currents in a manner well known in the art. For an exampleof a suitable arrangement for recording varying signals on magnetictape, reference may be made to Patent 1,944,238 to Clarence N. Hickman,issued January 23, 1934. The tape is preferably moved in the gap II atthe speed at which the signals were recorded, any suitable means, suchas the driving means shown in the Hickman patent, being suitable forthis purpose.

For the sake of clarity in describing the oathode ray device |3,reference will now be made to Fig. 3 which shows a longitudinalcross-sec tion of the cathode ray device l3 taken from the top. Theposition of the yoke surrounding the tube is indicated by dotted linesin this figure. The device l3 preferably comprises a gas-tight containerl6 enclosing a cathode an accelerating anode l8, a second anode IS, apair of magnetic pole-pieces 20 and 2|, and a target or screen T.

The cathode l1 comprises a metal cylinder which is heated by a filament22 supplied with current by a suitable source of potential 21. Thecathode may have a coating of material which produces a large electronemission when heated.

The accelerating anode l8 comprises a long cylinder surrounding thecathode l1 and having an aperture plate 23 therein. The plate 23 islocated near the end of the cylinder remote from the cathode.Accelerating anode |9 comprises a cylinder around one end of thecylinder l8 and extending toward the target T. The cylinder |9 has adiaphragm 24 at the end near the target T. This diaphragm 24 has anaperture 25 therein which is of substantially square or rectangularcross-section. The anodes l8 and I9 together comprise an electron lenssystem which focuses a beam of electrons of a cross-section determinedby the shape of the aperture 25 upon the target T, The inside of thecontainer I6 contains a coating 26 of aquadag, this coating extendingsubstantially from the region of the target T to the polepieces 20 and2|. Accelerating anode |8 is placed at a positive potential with respectto the cathode IT by means of a source of potential such as the battery28, and the anode |9 is placed at a positive potential with respect tothe anode l8 by means of a source of potential such as the battery 29.The screen 26 is preferably placed at the same potential as the anodeI9.

The cathode I1 and the accelerating anodes l8 and H! are supported froma bifurcated press 30. Supporting wires 3| support the anode from theoutstanding portionsof the bifurcated press. A flange 32 of insulatingmaterial surrounds the end of the cylinder 3 near the target T and thecylinder H! is partially supported from this flange by supporting wires33, the cylinder I9 being further supported by a disc 34 which isfastened to the pole-pieces 20 and 2| by screws 35.

The target T comprises plates 40 and 4|, a screen or partition member 42located between the plates, and a mesh or grid member 43 parallel to theplates and located a small distance in front thereof. The plates 40 and4| are electrically connected to the primary winding 44 of an outputtransformer 45, the secondary winding 46 of which may be connected toany suitable circuit. The partition member 42 is electrically connectedto the mesh screen or grid member 43 and to the mid-point of the primarywinding 44 of the transformer 45 through a source of potential 41 whichis so poled that the partitionmember 42 and the screen 43 are placed ata negative potential with respect to the plates 40 and 4|. The negativeterminal of battery 41 is also connected to the coating 26 and to thesecond accelerating anode l9.

Surrounding the cathode ray device l3 and completing the magneticcircuit |2 between the magnetic tape I0 and the cathode ray beam (whichis adapted to pass between the pole-pieces 20 and 2|) is a yoke 50 ofsoft iron which is shown diagrammatically in Fig. 1 and in furtherdetail in Fig. 2. Supported in grooves in the two parts of the yoke 50are metallic pole-pieces and 52 which are so placed as to leave a verynarrow air-gap through which the magnetic tape I0 is adapted to pass.The yokes 50 terminate around the cathode ray tube l3 adjacent thepolepieces 2|! and 2| located within the tube.

The magnetic circuit l2 thus has two aps therein, the gap H which islarge enough for the magnetic tape to pass therethrough and the gap 53through which the beam generated by the cathode and accelerated andfocussed by the anodes l8 and H! is adapted to pass on its path to thedivided target T. a

The operation of the electronic pick-up arrangement shown in Fig. 1 willnow be described. Electrons are emitted by the cathode l'I, acceleratedby the anodes I8 and I9, and focused by these anodes in cooperation withthe coating into a beam of electrons which is directed toward the targetor screen T; A relatively low voltage is used to accelerate this beamas, for example, of the order of 100 volts. Because of this low voltagethe beam may be appreciably bent when it passes between the pole-pieces20 and 2| due to the magnetic flux present in the gap between thepole-pieces. Let it be assumed that a portion of the tape l0 having nosignals impressed thereon is in the gap l of the magnetic circuit l2.When this condition exists, the electron beam is not bent as it passesbetween the pole-pieces 20 and 2| and the energy of the beam is evenlydivided between the two target plates 40 and 4|. Due to the fact thatthe plates 40 and 4| are hooked up in push-pull fashion, no current willflow in the secondary winding 46 of the transformer 45. Now assume thatthe portion of the tape l0 having a signal current impressed thereon ispassing through the gap The flux from this magnetic tape thus passesthrough the magnetic circuit l2 and causes the beam to be bent in such amanner that its energy is divided unequally between the two plates 40and 4|. The balance between the currents flowing in the primary winding44 of the transformer 45 is thus disturbed and an output current flowsin the secondary winding 46 of the transformer 45 which is proportionalto the signal magnetically recorded on the tape.

The accompanying drawing shows one preferred dimensioning of the variousparts of a structure in accordance with the invention. The main diameterof the actual cathode ray tube shown is one and three-fourths inches,all dimensions in the drawing being scaled down in the same ratio.

In order to more fully study the operation of this device let it beassumed that the recording electromagnet used with the ordinary magnetictape recorder induces magnetization proportional to the amplitude of thecurrent flowing in the coils. Suppose that an alternating current of theform a=A sin or. is put into the recorder. The intensity of theresultant flux through the tape will be rp=KA sin wt. The voltagedelivered amass? Various modifications may obviously be made y he-Pickpcoils that an ordinary electromagnetic pick-up device isused) willbegiven by the equation ;=Agoi cos cot 'lhus with this form ofquenciesareshiftedinphasebyflodegrees and the output is proportional Asthe tape moves through the gap H, its flux is guided by the yoke 50 tothe cathode ray tube l3 where it deflects the electron beam by shiftingit away from anode plate towards the other plate 4| and vice versa,depending upon the secondary 48 and 4| to pick-up device all freanair-gap of small area,

without departing from the spirit of the'invention, the scope of whichis defined by the appended claims.

What is claimed is:

1. The combination with an electron beam discharge tube of beamdeflecting means comprising a magnetic flux path terminating at one endwithin the tube in the vicinity of the beam, a magnetic signal recordmember adiacent the other end of ing relative and said record member.

2. The combination with an electron beam discharge tube of beamdeflecting means comprising a magnetic flux path of high permeabilityterminating at one end within the tube in a pole-piece in the vicinityof said beam and at the other end in a surface of area small enough toread a magnetic tape record of the kind used to record speech-and othersignals.

3. The combination with a magnetic circuit,

of an electric beam discharge tube in a gap in said circuit, a magneticsignal record member in a second gap in said circuit, and means forproducing relative movement between said circuit and said member.

yoke arranged so as to define of an electron beam discharge tube locatedbetween the legs of said yoke, said discharge tube having therein a pairof pole-pieces of magnetic pieces have a narrow gap therebetween throughwhich said beam passes.

5. In combination, a magnetic tape record of a varying current,

of said flow of electrons.

6. A cathode ray device comprising means for generating a beam ofelectrons, a pair of anode members in the path of said beam, each anodewith the successive vanations of said record material which pole- 8. Acathode ray device comprising means for generating a. beam of electrons,a pair of anode members in the path of said beam, each anode being inthe neutral position of the beam contacted by substantially half theelectrons of said beam, a magnetic record member, a, path of highpermeability between said magnetic record and said beam for causing saidbeam to be deflected in accordance with the successive variations ofsaid record member to thereby change the dis tribution of electronsbetween the anode members, and an external circuit connected to saidanode. v

9. The combination with a yoke of magnetic material of a pair 01'tapered pole-pieces within an electric discharge tube, and adjacent therespective legs of said y'oke, said yoke having a gap thereinexternal'to said tube, and means within said tube for directing theelectric discharge between said pole-pieces.

10. The combination with a yoke of magnetic material of a pair oftapered pole-pieces within an electric discharge tube and adjacent therespective legs of said yoke, said yoke having a gap therein external tosaid tube, means within said tube for directing the electric dischargebetween said pole-pieces, and means for applying a varyingmagneto-motive force to said yoke from within said external gap.

11. The combination with a yoke of magnetic material of a pair oftapered pole-pieces within an electric discharge tube, said yoke havinga gap therein external to said tube, means within said tube fordirecting the electric discharge between said pole-pieces, means forapplying a varying magneto-motive force to said yoke from within saidexternal gap, and means for utilizing the resultant change of directionof the electric discharge toset up corresponding current variations in acircuit external to said tube.

12. The combination with a yoke member of magnetic material, a vacuumtube extending between the extremities of the legs of said member, andtapered members of magnetic material mounted inside said vacuum tube insuch position that their outer extremities register respectively withthe extremities of said yoke member and their inner extremities arespaced apart to form a small gap therebetween.

13. A cathode ray tube comprising a cathode for emitting electrons, atarget, means for forming said electrons into a beam and directing saidbeam toward said target and members of magnetic material mounted betweensaid cathode and said target, each member consisting of a taperedelement having its outer and larger port'on shaped to conform to thecontour of the tube wall and its inner and smaller portion ad-' jacentthe path of the cathode beam.

14. The combination with an electron beam discharge tube, of means fordeflecting said beam comprising a magnetizable element having differentportions differently magnetized, a magnetic flux path extending frompole pieces within the tube in the vicinity of said beam to the vicinityof said element, and means for moving said element so that said portionsin succession vary the flux of said flux path.

15. The combination with an electron beam discharge tube, of a magneticflux path including a yoke of material of high magnetic perme-' abilityand having a gap through which said beam passes and a second gap at adistance from said beam, a magnetic record element located in saidsecond gap, and means for moving said element through said second gap.

16. A device for reading magnetic record elements-comprising thecombination with an electron beam discharge tube, of a magnetic flux Iportions of said legs path including a yoke of materialoi highpermeability, said yoke being divided into two legs and each leg beingdivided into two parts with one part of each being external to said tubeand the other in alinement therewith within said tube, both said partsbeing shaped to closely fit the contour of the tube wall and beingsubstantially in contact therewith, said parts within said tube beingspaced to form a narrow gap between which the electron beam passes, andsaid external parts being spaced to form another narrow gap suitable forhaving a magnetic record element passed therethrough.

17. The combination with an electron beam discharge tube, of a magneticflux path including a yokeof material of high magnetic permeabilityoutside said-tube, each of the two legs of said yoke terminating atopposite sides of the wall of said tube and conforming to the shape ofsaid wall, tapered pole-pieces within said tube and respectively inalinement with said shaped outside portions of said legs and shaped tofit the wall of said tube, said pole-pieces being positioned to form agap therebetween, means for forming and projecting a beam of electronsthrough said gap, the dimension of said gap perpendicular to the axis ofsaid beam being only slightly greater than the dimension of the beam inthat direction, and a target for said beam at a distance from said gapmany times the dimension of said gap in the direction of the axis of thebeam, each of said legs being tapered at its extremity opposite the oneat said wall and forming with the corresponding extremity of the otherleg a small gap of the order of the size of said first-mentioned gap.

18. The combination with an electron beam discharge tube of a magneticflux path including a yoke of material of high magnetic permeabilityoutside said tube, each of the two legs of said yoke terminating atopposite sides of the wall of said tube and conforming to the shape ofsaid wall, tapered pole-pieces within said tube and respectively inalinement with said shaped outside and shaped to fit the wall of saidtube, said pole-pieces being positioned to form a gap therebetween,means for forming and projecting a beam of electrons through said gap,the dimension of said gap perpendicular to the axis of said beam beingonly slightly greater than the dimension of the beam in that direction,and a target for said beam at a distance from said gap many times thedimension oi said gap in the direction of the axis of the beam, each ofsaid legs being tapered at its extremity opposite the one at said walland forming with the corresponding extremity of the other leg a smallgap of the order of size of said first-mentioned gap, the dimensions ofsaid gap within said tube in the direction of the axis ofthe beam beingmuch greater than its dimensions at right angles thereto. a

19. The combination with an electron beam discharge tube of a magneticflux path including a yoke of material of high magnetic permeabilityoutside said tube, each of the two legs of said yoke terminating atopposite sides of the wall of said tube and conforming to the shape ofsaid wall, tapered pole-pieces within said tube and respectively inalinement with said shaped outside portions of said legs and shaped tofit the wall of said tube, said pole-pieces being positioned to form agap therebetween, means ifor forming and projecting a beam of electronsthrough said gap, the dimension of said gap perpendicular to ammo-r theaxis of said beam being only slightly greater than the dimension of thebeam in that direction, and a target for said beam at a distance fromsaid gap many times the dimension of said gap in the direction of theaxis of the beam, each of said legs being tapered at its extremityopposite the one at said wall and forming with the correspondingextremity of the other leg a small gap of the order of size of saidfirst-mentioned gap, said means for producing and projecting said beamcomprising-a gun structure and means for supporting said on said gunstructure.

20. The combination with an electron beam discharge tube comprising anevacuated container substantially free of gas content enclosing meansfor generating a beam of electrons, a target comprising two elementsspaced from each other, and a pair of pole-pieces on opposite sides ofthe beam, and means outside said enclosure for deflecting said beam fromone of said target elements to the other so that the energy of the beamis divided between said elements comprising a magnetizable elementhaving different portions difierently magnetized, and magnetic fluxpaths extending from the vicinity of said pole-pieces within the tube tothe vicinity of said magnetizable element, and means for moving saidmagnetizable element so that said difierently magnetized portions insuccession vary the flux in said paths to vary the distribution of saidbeam between said target portions.

21. A cathode ray device comprising means for generating a beam ofelectrons, a target for said beam having two portions displaced fromeach other, a transformer, means for connecting the primary of saidtransformer between said two portions of said target, means forconnecting substantially the midpoint of said primary to said beamgenerating means, means for connecting the secondary of said transformerto an output circuit, a pair of pole-pieces within said tubebepole-pieces within said tube tween said beam generating means and saidtaret member, a magnetic signal record member, a magnetic flux pathcomprising two leg members of magnetic material extending from a re gionclosely adjacent said pole-pieces to a region on opposite sides of andclosely adjacent the magnetic record member, and means for moving saidmagnetic record member in the gap created by the space between said legsso that said beam is caused to divide its energy between the twoportions of the target member in such a manner that an amplified outputcurrent is produced in the secondary of said transformer.

22. A cathode my device comprising means for generating a beam ofelectrons, a target for said beam having two portions displaced fromeach other, a transformer, means for connecting the primary of saidtransformer between said two portions of said target, means forconnecting substantially the mid-point of said primary to said beamgenerating means, means for connecting the secondary of said transformerto an output circuit, a pair of pole-pieces within said tube betweensaid beam generating means and said target member, a magnetic signalrecord member, a magnetic flux path comprising two leg members ofmagnetic material extending from a region closely adjacent saidpole-pieces to a region on opposite sides of and closely ad- Jacent themagnetic record member, means for moving said magnetic record member inthe gap created by the space between said legs so that said beam iscaused to divide its energy between the two portions of the targetmember in such a manner that ,an amplified output current is produced inthe secondary of said transformer, and means between said two portionsof said target for preventing secondary electrons caused to be emittedby the primary beam impinging upon each of said target portions frompassing to the other of said target portions.

